Modern helicopter configurations typically include a plurality of individual main rotor blade assemblies which are each coupled to a main rotor shaft assembly. An engine rotates the main rotor shaft which, in turn, rotates or spins the attached main rotor blade assemblies to provide lift and thus, flight for the helicopter. The pitch of each of the main rotor blade assemblies is adjustable to facilitate the forward movement and control of the helicopter.
The main rotor blade assemblies are each coupled to the main rotor shaft assembly in such a manner as to accommodate several degrees of freedom of motion. Previously, this coupling utilized a hinged connection. However, in modern helicopters, each of the main rotor blade assemblies is connected to the main rotor assembly through a flexible elastic joint type of connection.
These flexible joint connections between each of the main rotor blade assemblies and the main rotor assembly are required due to the wide variation and ever changing loads carried be the main rotor blade assemblies. More specifically, the main rotor blade assemblies must adjust from a no load condition (parked) to a fully loaded flight condition. During flight, the main rotor blade assemblies must react both the centrifugal force as well as the load from the helicopter. Various in flight loads must also be reacted.
To accommodate these loads, each of the main rotor blade assemblies is designed with a certain degree of relatively free movement or flexibility in a direction generally parallel to the main rotor shaft. This movement is often referred to as "flap" or main rotor blade flap. The flexible type joint connections are designed to accommodate this movement. However, over-flexing or flap movement beyond the flexible limit of the joint connection may cause serious damage to the joint connection as well as the main rotor assembly.
When the helicopter is in a parked condition, the main rotor assembly is static and each of the rotor blade assemblies is stationary and generally unloaded. In this condition, gravity pulls each of the main rotor blade assemblies down to their lowest possible position. This is typically called rotor blade droop. Generally, a droop stop mechanism or other mechanical stop is provided to prevent each of the main rotor blade assemblies from drooping so low as to overextend or otherwise overload each of the flexible joint type connections.
When the main rotor assembly is rotating, each of the main rotor blade assemblies is forced upwardly by the centrifugal force and other loads. This force pivots the main rotor blade assemblies at their respective flexible joint connections and lifts than off of the droop stop mechanism. The centrifugal force, which is typically large in comparison to the generally vertical flight loads, prevents the main rotor blade assemblies from moving upwardly beyond the flexible limit of the flexible joint type connections. However, when the helicopter is parked, their is no mechanism to prevent the main rotor blade assemblies from flapping or otherwise being moved upwardly and over extending the flexible joint type connections. This is a particular concern during windy conditions, when the weight of each rotor blade assembly is not enough to resist the wind generated lift forces.
Another problem with the free flapping of the main rotor blade assemblies occurs during storage or non flight transportation operations. During these operations, the main rotor blade assemblies are often bounced or otherwise moved off of their droop stop mechanisms. This bouncing can over extend the flexible joint type connection causing damage as previously described. In addition, these operations often require that each of the main rotor blades be folded aft or rearward to a secure storage position.
The ability to fold the main rotor blades is highly desirable and sometime a mandatory operational feature. However, many modern helicopters have no mechanism to restrain the main rotor blades from flapping up or down during the folding process. This problem is hazardous to both personnel and the aircraft hardware. The problem is magnified if the folding operation is performed in a windy environment.